The present invention relates to a method and apparatus for cutting a wire formed on a semiconductor substrate by scanning the wire with a focused ion beam.
Semiconductor integrated circuits (e.g., LSI) have become highly integrated and provided with higher functions over recent years. When developing an LSI, logic for many circuits must be corrected. More specifically, when a circuit does not function due to a logic error or a layout error, a focused ion beam process is performed to cut a wire at the location where the error occurred. There is a demand for technology that ensures the cutting of the wire with a focused ion beam.
A device (FIB device) for cutting a wire that is formed on a semiconductor substrate with a focused ion beam is known in the prior art. An example of such an FIB device was described on the Internet (URL, http://www-6.ibm.com/jp/chips/v5_/mn51011.html) in an online article titled “Achieving Quick Design Debugging With Circuit Correction Function Using Focused Ion Beam Technique” published by IBM on Jun. 23, 1999 (available in searches as of Sep. 16, 2003).
Referring to FIGS. 1 and 2, an FIB device scans a wire 2 with a focused ion beam to form a rectangular pattern that extends across the wire 2. During scanning, stray material 2a produced when cutting the wire 2 is dispersed radially and adhered to the walls of a processed portion 3. This may result in unintended short-circuiting between wires. To prevent such short-circuiting, the above article describes a cleaning technique using halogen-containing gas, or gas assisted etching (GAE). In this technique, the halogen-containing gas is injected toward the surface of a semiconductor substrate. The stray material 2a reacts with the gas molecules in the halogen-containing gas and forms a volatile product. This minimizes the adherence of the stray material 2a to the processed portion 3.
When cutting aluminum wires of an LSI with the FIB device, powdered stray material adheres to the walls of the processed portion. In such a case, unintended short-circuiting between wires seldom occur.